Intermediate heat exchanger-incorporated type steam generator

ABSTRACT

An intermediate heat exchanger-incorporated type steam generator having two functions of an intermediate heat exchanger and a steam generator and capable of simplifying a secondary cooling system.  
     An intermediate heat exchanger tube  20  and a steam generating heat exchanger tube  22  are disposed separately in a vessel  10  storing a secondary coolant  14  therein, and a pump mechanism for forcibly circulating the secondary coolant in the vessel. The pump mechanism is made of an electromagnetic pump mechanism formed by an electromagnetic driving coil  24  provided on an outer circumference of the vessel and a magnetic core  26  attached to an inner cylinder  12  disposed in the vessel. At least one porous plate or slotted plate  18  is preferable disposed between the intermediate heat exchanger tube and steam generating heat exchanger tube.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to an intermediate heatexchanger-incorporated type steam generator provided with anintermediate heating exchanger tube and a steam generating heatexchanger tube separately in the interior of a vessel, and having afunction of generating steam by forcibly circulating a secondary coolant(intermediate coolant) in the vessel to thereby subject the coolant toheat exchange. This technique is especially useful for a steam generatorin a liquid sodium-cooled reactor.

[0002] In a fast breeder reactor using liquid-metal sodium as a coolant,electric power is generated by a turbine, so that a steam generatoradapted to generate steam with the heat of sodium is employed. Thissteam generator is generally constructed so that liquid sodium is passedthrough the interior of a heat exchanger tube and water around the heatexchanger tube is heated and turned into steam. However, sodium has theproperty of violently reacting with water. Therefore, a secondarycooling system using an intermediate heat exchanger and a secondarycoolant of sodium is generally employed so as to prevent the influenceof the interaction of water with sodium from being exerted on a reactorcore in the unlikely event of the breakage of the heat exchanger tube inthe steam generator. Namely, the reactor core is cooled with a primarycoolant of sodium, and a secondary coolant of sodium is heated with theheat of the primary coolant sodium in the intermediate heat exchanger.The secondary coolant sodium is then guided into the steam generator,where water is heated with the heat of the secondary coolant sodium andturned into steam.

[0003] As compared with a structure in which steam is generated in asteam generator by directly using the primary coolant sodium which haspassed through a reactor core, the above-described secondary coolingsystem is advantageous in that the influence exerted on the reactor coreis little when the heat exchanger tube should be broken, and in thatactivated sodium does not leak out. On the other hand, there is requiredvarious kinds of equipment in the secondary cooling system including anintermediate heat exchanger, a primary pump, piping installation,auxiliary equipment such as measurement control equipment, preheatingequipment, sodium purification equipment and the like, a dump tank andso on. Also, since a large quantity of secondary coolant sodium isnecessary, the cost increases. Moreover, a large space in which thesevarious kinds of equipment are installed is also needed.

SUMMARY OF THE INVENTION

[0004] An object of the present invention, therefore, is to provide anintermediate heat exchanger-incorporated type steam generator havingboth functions of an intermediate heat exchanger and a steam generatorso that a secondary cooling system can be simplified and a quantity ofsodium coolant and an installation space required for the secondarycooling system can be greatly reduced.

[0005] Another object of the present invention is to provide anintermediate heat exchanger-incorporated type steam generator capable ofsecuring a high safety even in the unlikely event of the breakage of aheat exchanger tube.

[0006] According to the present invention, there is provided anintermediate heat exchanger-incorporated type steam generatorcomprising: a vessel storing a secondary coolant therein, anintermediate heat exchanger tube and a steam generating heat exchangertube separately disposed in the vessel, and a pump mechanism forforcibly circulating the secondary coolant in the vessel.

[0007] According to the present invention, there is also provided anintermediate heat exchanger-incorporated type steam generatorcomprising: a cylindrical vessel storing a secondary coolant of liquidsodium therein, an inner cylinder disposed in the cylindrical vessel toform a flow passage of the secondary coolant and divide the flow passageinto flow passage portions inside and outside the inner cylinder, ahelical coil-shaped steam generating heat exchanger tube disposed in anupper portion of the interior of the inner cylinder, an intermediateheat exchanger tube disposed separately from the steam generating heatexchanger tube in a lower portion of the interior of the inner cylinder,and an electromagnetic pump mechanism formed by an electromagneticdriving coil provided on an outer circumference of the cylindricalvessel and a magnetic core attached to the inner cylinder, whereby thesecondary coolant is forcibly circulated in the vessel so that thesecondary coolant flows upward in the flow passage portion inside theinner cylinder and flows downward in the flow passage portion outsidethe inner cylinder.

[0008] In the steam generator described above, it is possible to dividethe flow passage portion between the cylindrical vessel and the innercylinder into a plurality of parts by a plurality of radially disposedpartition plates. In such a case, the electromagnetic driving coil isminiaturized and a plurality of miniaturized electromagnetic drivingcoils are provided on the outer circumference of the cylindrical vessel.

[0009] In the preferred embodiment of the present invention, at leastone porous plate or slotted plate is disposed between the intermediateheat exchanger tube and the steam generating heat exchanger tube,whereby the influence of the breakage of one of these heat exchangertubes is not exerted on the other. In the case where a plurality ofporous plates or slotted plates are disposed, they should be positionedwith a space from each other.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010]FIG. 1 is a longitudinal sectional view showing an embodiment ofthe intermediate heat exchanger-incorporated type steam generatoraccording to the present invention.

[0011]FIG. 2 is a sectional view taken along the arrowed line x-x inFIG. 1.

[0012]FIG. 3 is a sectional view showing another embodiment of thepresent invention.

PREFERRED EMBODIMENTS OF THE INVENTION

[0013]FIG. 1 illustrates an embodiment of the intermediate heatexchanger-incorporated type steam generator according to the presentinvention, which is suitable for a secondary cooling system for asodium-cooled fast breeder reactor. FIG. 1 is a longitudinal sectionalview, and FIG. 2 a sectional view taken along the arrowed line x-x inFIG. 1. A cylindrical vessel 10 having a bottom and an upper lid isprovided in the interior thereof with an inner cylinder 12 coaxiallywith and in a spaced manner with respect to the cylindrical vessel 10.The length (height) of the inner cylinder 12 is smaller than that(height) of the vessel 10, and upper and lower ends of the innercylinder 12 are sufficiently spaced from the upper lid and the bottom ofthe cylindrical vessel 10, respectively. The cylindrical vessel 10stores therein a secondary coolant (liquid sodium) 14, and an upper freeliquid level is covered with a cover gas (inert gas) 16. The innercylinder 12 fulfils the function of separating a flow passage into partson the inner and outer sides thereof, and the flow passage portioninside the inner cylinder forms an upward flow region, while the flowpassage portion outside the inner cylinder (i.e. between the cylindricalvessel 10 and the inner cylinder 12) forms a downward flow region.Accordingly, the free liquid level is set so that the upper end of theinner cylinder 12 is completely submerged in the secondary coolant 14.

[0014] Porous plates 18, which may be replaced with slotted plates, areprovided in the substantially central portion of the interior of theinner cylinder 12 with respect to the vertical direction thereof. Thepore diameter or slot width should be set to levels at which the liquidsodium can pass therethrough freely. The porous plates or slotted plates18 may be provided singly, or plurally in a spaced manner. In theembodiment as shown in FIG. 1, two porous plates 18 are fixedhorizontally in the interior of the inner cylinder 12 with a spacebetween the plates. A helical coil-shaped intermediate heat exchangertube 20 is disposed in the inner portion of the inner cylinder 12 whichis below the lower porous plate 18, and a helical coil-shaped steamgenerating heat exchanger tube 22 in the inner portion of the innercylinder 12 which is above the upper porous plate 18. In the presentinvention, since these heat exchanger tubes 20, 22 are formed helically,these heat exchanger tubes can be made compact and held easily in theinterior of the cylindrical vessel 10. Further, by disposing the steamgenerating heat exchanger tube 22 and the intermediate heat exchangertube 20 in the vertically positional relation, the flow direction of thesecondary coolant 14 around these heat exchange tubes 20, 22 in theinterior of the inner cylinder 12 is set upward, and the heat exchangeefficiency is thereby improved.

[0015] An electromagnetic driving coil 24 is provided on an outercircumference of the cylindrical vessel 10, and a magnetic core 26attached to the inner cylinder 12. These coil and core form anelectromagnetic pump, which drives the secondary coolant (liquid sodium)14. The heat exchange efficiency is improved and the dimensions of thesteam generator are reduced by forcibly circulating the secondarycoolant 14 in the cylindrical vessel 10. By providing theelectromagnetic driving coil 24 on the outermost circumferential portionof the cylindrical vessel 10 in such a manner, the driving coil 24 ismade compact and integrated with the cylindrical vessel 10. Furthermore,the provision of the electromagnetic driving coil 24 on the outermostcircumferential portion of the cylindrical vessel 10 enables not only aself-cooling operation but also a forced cooling operation to be carriedout.

[0016] The primary coolant (liquid sodium) heated as it flows throughthe reactor core reaches the intermediate heat exchanger-incorporatedtype steam generator, flows through the interior of the intermediateheat exchanger tube 20 and transmits heat to the secondary coolant(liquid sodium) 14 existing around the intermediate heat exchange tube20. The thus heated secondary coolant (liquid sodium) 14 flows up in theinner cylinder 12, passes through the pores or slots of the porousplates or slotted plates 18, flows around the steam generating heatexchange tube 22, and transmits heat to the water flowing through theinterior of the steam generating heat exchanger tube 22. The waterpassing through the steam generating heat exchange tube 22 is therebyheated, and turned into steam, which flows out from the intermediateheat exchanger-incorporated type steam generator toward a turbinegenerator and the like.

[0017] In the present invention, the efficiency of the heat transferfrom the primary coolant (liquid sodium) in the intermediate heatexchanger tube 20 to the secondary coolant (liquid sodium) 14, and thatfrom the secondary coolant (liquid sodium) 14 to the water in the steamgenerating heat exchanger tube 22 are improved by forcibly fluidizingand circulating the secondary coolant (liquid sodium) 14 in the interiorof the cylindrical vessel 10 by using the electromagnetic pumpmechanism. In the illustrated embodiment, an induction typeelectromagnetic pump mechanism having a simple duct structure and notrequiring an electrode to which an electric current is supplied from theoutside is formed by the electromagnetic driving coil 24 provided on theouter circumference of the cylindrical vessel 10 and the magnetic core26 attached to the inner cylinder 12, so that the secondary coolant(liquid sodium) 14 in the cylindrical region between the inner cylinder12 and cylindrical vessel 10 can be driven downward. The electromagneticdriving coil 24 is a coil for driving a conductive fluid (secondarycoolant sodium) which is formed by spatially shunt winding, for example,a 3-layer winding, and adapted to generate a traveling magnetic field bysupplying a 3-phase alternating current thereto. The magnetic core 26fulfils the functions of strengthening the magnetic field and improvingthe driving efficiency.

[0018] Even when a hydrogen gas is generated due to an interaction ofthe water or steam flowing in the steam generating heat exchanger tube22 with the secondary coolant (liquid sodium) 14 which occurs in theunlikely event of the breakage of the steam generating heat exchangertube 22, the porous plates or slotted plates 18 fulfill the functions ofprotecting and isolating the intermediate heat exchanger tube 20 so thatthe influence of such an interaction does not cause the soundness of theintermediate heat exchanger tube 20 to be lost.

[0019] Even when a material reactive with the primary coolant is used asthe secondary coolant, the porous plates or slotted plates can alsofulfill the functions of preventing the influence of an interaction ofthe primary coolant and the secondary coolant, which occurs when theintermediate heat exchanger tube 20 is broken, from being exerteddirectly on the steam generating heat exchanger tube 22 and causing thesoundness of the heat exchanger tube 22 to be lost.

[0020] When it is necessary to cool the electromagnetic driving coil 24of the electromagnetic pump mechanism, the outer circumference of thecylindrical vessel 10 is covered with an insulating material (notshown), and the electromagnetic driving coil 24 is provided on the outerside of the insulating material. Such an arrangement can be taken, sincethe electromagnetic coil 24 is provided on the outermost surface of thecylindrical vessel 10, and this arrangement enables the electromagneticdriving coil 24 to be self-cooled or forcibly cooled.

[0021]FIG. 3 shows another embodiment of the present invention. Thisfigure is a drawing prepared correspondingly to the drawing taken alongthe arrowed line x-x in FIG. 1 just as FIG. 2. To simplify thedescription of the embodiment, the same reference numerals as in FIG. 2will be assigned to the corresponding members. In this embodiment, theflow passage between the cylindrical vessel 10 and the inner cylinder 12is divided into a plurality of parts by a plurality of radially disposedpartition plates 30, and the electromagnetic driving coil 32 is alsominiaturized and provided plurally. In this embodiment, there is shownan example in which the flow passage is divided into eight flow passageportions by eight partition plates 30 and eight miniaturizedelectromagnetic driving coils 32 are separately arranged. In thisstructure, even the difficulty of manufacturing a large currentlarge-sized electromagnetic pump can be dealt with by combining aplurality of miniaturized electromagnetic driving coils 32 together, andthe advantages of easily manufacturing the miniaturized coils and easilycarrying out maintenance work thereof are obtained.

[0022] As being understood from the foregoing, the intermediate heatexchanger-incorporated type steam generator of the present invention canattain the same functions as those of a prior art secondary coolingsystem constituting an intermediate heat exchanger, a secondary piping,a secondary pump, a steam generator and the like. Moreover, thenecessary equipment and an installation space can be reduced greatly,and the length of piping can be shortened, as compared with the priorart secondary cooling system.

[0023] Further, in the present invention, one or more of the porousplates or slotted plates may be disposed between the intermediate heatexchanger tube and the steam generating heat exchanger tube. Such astructure can prevent an interaction of the primary coolant flowingthrough a reactor core with water or steam when either of these heatexchanger tubes is broken, and enables a sufficient safety to besecured.

What is claimed is:
 1. An intermediate heat exchanger-incorporated typesteam generator comprising: a vessel storing a secondary coolanttherein, an intermediate heat exchanger tube and a steam generating heatexchanger tube separately disposed in said vessel, and a pump mechanismfor forcibly circulating the secondary coolant in said vessel.
 2. Anintermediate heat exchanger-incorporated type steam generatorcomprising: a cylindrical vessel storing a secondary coolant of liquidsodium therein, an inner cylinder disposed in said cylindrical vessel toform a flow passage of the secondary coolant and divide said flowpassage into flow passage portions inside and outside said innercylinder, a helical coil-shaped steam generating heat exchanger tubedisposed in an upper portion of the interior of said inner cylinder, anintermediate heat exchanger tube disposed separately from said steamgenerating heat exchanger tube in a lower portion of the interior ofsaid inner cylinder, and an electromagnetic pump mechanism formed by anelectromagnetic driving coil provided on an outer circumference of saidcylindrical vessel and a magnetic core attached to said inner cylinder,whereby the secondary coolant is forcibly circulated in said vessel sothat the secondary coolant flows upward in said flow passage portioninside said inner cylinder and flows downward in said flow passageportion outside said inner cylinder.
 3. An intermediate heatexchanger-incorporated type steam generator according to claim 2,wherein said flow passage portion between said cylindrical vessel andsaid inner cylinder is divided into a plurality of parts by a pluralityof radially disposed partition plates, said electromagnetic driving coilis miniaturized and a plurality of said miniaturized electromagneticdriving coils are provided on the outer circumference of saidcylindrical vessel.
 4. An intermediate heat exchanger-incorporated typesteam generator according to any of claims 1 to 3, wherein at least oneporous plate or slotted plate is disposed between said intermediate heatexchanger tube and said steam generating heat exchanger tube, wherebythe influence of the breakage of one of these heat exchanger tubes isnot exerted on the other.